Volunteers search people who want to join the demonstration in Ramadi, 70 miles west of Baghdad, Iraq, Wednesday. Iraqi authorities have closed the country’s only border crossing with Jordan over security concerns, cutting a key route through a part of the country that has seen anti-government protests.

BAGHDAD — Iraqi authorities citing security concerns closed the country’s only border crossing with Jordan on Wednesday, cutting a key route through a part of the country where anti-government protests have been raging for weeks.

Residents of Anbar province, the center of the Sunni-led demonstrations, rejected the closure and accused the government of trying to pressure them to end their protests against Prime Minister Nouri al-Maliki’s Shiite-dominated administration.

“The closure ... serves only one purpose, and that is to damage the image of the protesters and depict them as troublemakers who want to make the lives of Iraqis more difficult,” one of the protest organizers, Saeed Humaim, told The Associated Press. “We will stand firm on our demands, and we will not be shaken by this irresponsible act.”

Many Sunnis in Iraq complain of discrimination by the Shiite-led government. The mass protests in Anbar — and increasingly elsewhere in the country — are the largest and most sustained demonstration of Sunni discontent since the 2003 U.S.-led invasion. Sectarian tensions frequently boil over into bloody attacks, nowadays mostly by Sunni extremists against Shiite residents and pilgrims, threatening the country’s stability.

The prime minister’s spokesman, Ali al-Moussawi, did not specify the nature of the security fears that he said prompted the move. He denied that the closure was intended to pressure protesters, saying officials were responding to intelligence information.

The highway from Baghdad to the Jordanian border runs through Anbar, a vast Sunni-dominated province in Iraq’s western desert. The heavily traveled road, which extends about 350 miles from the border to Baghdad, is one of Iraq’s most vital routes for travelers and trade.

An Associated Press journalist crossing the border around midnight reported a chaotic scene ahead of the closure. Border police were seen yelling at drivers and truckers to hurry across, and many were let into Iraq without the customary inspections.

Dhari Arkan, the deputy governor of Anbar, said the provincial council plans to sue the government over the closure, which he said was imposed without local officials’ knowledge.

A Jordanian border official said Iraq sealed the frontier unilaterally from the Iraqi side in the morning, without giving a clear explanation. He said the Jordanians were told it was “a temporary measure due to unspecified domestic reasons.”

The official declined to be identified, saying he was not allowed to make statements to reporters.

Anbar has been the center of more than two weeks of demonstrations along the highway by Sunni residents angry over perceived second class treatment by the Shiite-dominated government.

About 2,000 people rallied near the provincial capital, Ramadi, on Wednesday, with some burning Iranian flags — a reference to what they see as the neighboring Shiite nation’s influence over the Iraqi government.

Ahmed al-Alawani, a lawmaker from the Iraqiya bloc, which ran against the prime minister’s coalition in the last election, was among the protesters at the Ramadi sit-in. He described the border closure as “a desperate move by the government to deter the protesters from continuing their struggle for their legitimate rights.”

The ongoing demonstrations have blocked the highway near Ramadi, forcing motorists to take circuitous and potentially dangerous detours.

The protests erupted after the arrest of bodyguards assigned to Finance Minister Rafia al-Issawi, one of the central government’s most senior Sunni officials.

They have since spread to other areas populated by Iraq’s minority Sunnis, who dominated Saddam Hussein’s government until it was ousted in the U.S.-led invasion. Many Sunnis feel they have been mistreated by the central government and unfairly targeted by tough state security laws.